Etymologies

(American Heritage® Dictionary of the English Language, Fourth Edition)

The sound is very commonly made by infants, and is interpreted by parents as a reference to themselves. (Wiktionary)

Abbreviation. (Wiktionary)

Examples

_Ma ma ma ma ma ma ma ma ma ma_, the Chinese stammeringly say, and if the pitch and tone of each _ma_ are right, the meaning of the apparent repetition is, "Does Mother scold the horses, or will the horses scold Mother?"

Was it not Scarron who wrote a poem, 'A Guillemette, chienne de ma soeur, 'but quarrelling with his sister just as the volume was about to appear, put in the _errata_,' For _chienne de ma soeur_ read _ma chienne de soeur_ '!

a resemblance to each other, and then also commences for them that annoyance to which so many English children have been subjected, from generation to generation down to our time: the difficulty of knowing when to say _mon_ and _ma_ -- "kaunt dewunt dire moun et ma" -- that is how to distinguish the genders.